Fundus imaging apparatus and control method

ABSTRACT

A fundus imaging apparatus selects a focal position detection method in accordance with whether a diopter correction lens is inserted in an optical path of an imaging optical system that includes an imaging unit; and detects a focal position based on a signal from the imaging unit according to the selected focal position detection method.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fundus imaging apparatus and acontrol method.

2. Description of the Related Art

In order to capture a suitable fundus image using a fundus camera, it isnecessary to focus on the fundus of each eye individually. This isbecause different eyes to be examined have different degrees ofrefraction. A fundus camera having an autofocus function has beenproposed as a camera designed to facilitate such a focusing operation.In general, when imaging the fundus of an eye, such a fundus cameraperforms focusing by using a focus lens placed in an observation opticalsystem and focus indices which are driven in synchronism with the focuslens.

In this case, if a diopter correction lens for correcting strong myopiaor hyperopia is inserted in the observation optical system, the opticalrelationship between split and focus changes. That is, if a dioptercorrection lens is inserted in the observation optical system, since theoptical relationship between the focus lens and the focus indicesdeteriorates, it is impossible to perform focusing by using the focusindices. This makes it necessary for the examiner to manually performfocusing while observing an actual fundus image. Japanese PatentLaid-Open No. 2011-189063 has disclosed an invention which facilitatesmanual focusing operation by changing the operation sensitivity of afocus lens when a diopter correction lens is inserted.

It is however cumbersome for the examiner to perform such a manualfocusing operation. The lower the degree of skill of the examiner, themore time it takes for the focusing operation. This imposes a burden onthe person having their eye examined and may cause stress to the eyeitself.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, there is provided afundus imaging apparatus comprising: an illumination optical systemoperable to project illumination light on a fundus of an eye to beexamined; an imaging optical system operable to guide reflected lightfrom the fundus to an imaging unit; a driveable focus lens which isprovided in an optical path of the imaging optical system and which isoperable to focus the reflected light onto the imaging unit; a focusingunit operable to detect a focal position of the reflected light based ona signal from the imaging unit and to drive the focus lens according tothe detected focal position; and a selection unit operable to select afocal position detection method used by the focusing unit in accordancewith whether a diopter correction lens is inserted in the optical pathor not.

Also, according to another aspect of the present invention, there isprovided a method of controlling a fundus imaging apparatus comprising:selecting a focal position detection method in accordance with whether adiopter correction lens is inserted in an optical path of an imagingoptical system that includes an imaging unit; and detecting a focalposition based on a signal from the imaging unit according to theselected focal position detection method.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic arrangement of a fundus camera according to anembodiment;

FIG. 2 is a diagram for explaining the first focal position detectionmethod according to an embodiment;

FIG. 3 is a diagram for explaining the first focal position detectionmethod according to an embodiment;

FIG. 4 is a graph for explaining the second focal position detectionmethod according to an embodiment; and

FIGS. 5A and 5B are flowcharts showing an imaging sequence in the funduscamera according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

A preferred embodiment of a fundus imaging apparatus to which thepresent invention is applied will be described below with reference tothe accompanying drawings. According to the embodiment described below,there is provided a fundus camera which can execute autofocus operationeven in a state in which a diopter correction lens is inserted.

FIG. 1 shows an example of the schematic arrangement of a fundus camera100 as a fundus imaging apparatus according to this embodiment. Thefundus camera 100 includes an imaging light source part 101, anobservation light source part 102, an illumination optical system 103,an imaging/illumination optical system 104, and an imaging opticalsystem 105. The light beam emitted from the imaging light source part101 or the observation light source part 102 illuminates the fundusregion of the eye 27 through the illumination optical system 103 and theimaging/illumination optical system 104. The fundus region image is thenformed on an imaging device through the imaging/illumination opticalsystem 104 and the imaging optical system 105.

In the imaging light source part 101, reference numeral 11 denotes alight amount detection part, which is a sensor using known photoelectricconversion such as an SPC or PD (photodiode); 12, an imaging lightsource which emits light by applying a voltage to xenon (Xe) sealed in aglass tube and can obtain white light strong enough to record a fundusimage at the time of imaging; 13, an imaging condenser lens which is ageneral spherical lens; 14, an imaging ring slit which is a flat platehaving an annular opening; and 15, an imaging crystalline lens bafflewhich is also a flat panel having an annular opening.

In the observation light source part 102, reference numeral 16 denotesan observation light source which is a light source capable ofcontinuously emitting light such as a halogen lamp or LED, and emitsinfrared light depending on the characteristics of the device and/or afilter; 17, an observation condenser lens which is a general sphericallens; 18, an observation ring slit which is a flat plate having anannular opening; and 19, an observation crystalline lens baffle which isalso a flat panel having an annular opening.

The illumination optical system 103 relays the light beam generated bythe imaging light source part 101 and the observation light source part102 and forms index images for focusing on a fundus image. In theillumination optical system 103, reference numeral 20 denotes a dichroicmirror which transmits infrared light and reflects visible light.Therefore, the light beam of visible light generated by the imaginglight source part 101 is reflected by the dichroic mirror 20. The lightbeam of infrared light generated by the observation light source part102 is transmitted through the dichroic mirror 20, and guided to theillumination optical system 103. Reference numeral 21 denotes a firstillumination relay lens; and 23, a second illumination relay lens. Theselenses form ring illumination into an image on an eye to be examined.

Reference numeral 22 denotes a split unit which is constituted by asplit LED 221 for projecting focus indices (split images), a prism 222for splitting the light emitted from the LED 221, and a focus index mask223 indicating the outer shape of each focus index. The split unit 22includes a moving mechanism which shifts each focus index in theoptical-axis direction by moving these components in an arrow direction224 shown in FIG. 1 and an entering/retreating mechanism which causesthese components to enter the illumination optical system 103 at thetime of observation and to retreat from it at the time of imaging.Reference symbol M1 denotes a split shift driving motor; S1, a splitposition sensor which shifts the split unit 22 in the arrow direction224 to focus on each focus index and to detect the stop position; andM2, a split entering/retreating driving motor which causes the splitunit 22 to enter/retreat with respect to the illumination optical system103. The split entering/retreating driving motor M2 is controlled todrive the split unit 22 to enter the illumination optical system 103 toproject a split index in an observation image at the time of fundusobservation. At the time of imaging, the split entering/retreatingdriving motor M2 is controlled to drive the split unit 22 to retreatfrom the illumination optical system 103 so as to prevent each focusindex from being depicted in a captured image. Reference numeral 24denotes a cornea baffle which prevents unnecessary reflected light fromthe cornea of the eye to be examined from being depicted in a fundusimage.

The imaging/illumination optical system 104 projects an illuminationlight beam on the fundus of an eye 27 to be examined and guides a fundusimage of the eye to be examined. In the imaging/illumination opticalsystem 104, reference numeral 25 denotes a perforated mirror whoseperipheral portion is a mirror and central portion is a hole. The lightbeam guided from the illumination optical system 103 is reflected by themirror portion and illuminates the fundus of the eye to be examinedthrough an objective lens 26. The illuminated fundus image of the eye tobe examined returns to the objective lens 26 and is guided to theimaging optical system 105 through the hole in the central portion ofthe perforated mirror 25.

The imaging optical system 105 forms a fundus image of the eye to beexamined on the imaging device upon focus adjustment. In the imagingoptical system 105, reference numeral 28 denotes a focus lens which is alens for focus adjustment of an imaging light beam passing through thecentral hole of the perforated mirror 25 and which performs focusadjustment by moving in an arrow direction 281 in FIG. 1. Referencesymbol M3 denotes a focus lens driving motor; S3, a focus lens positionsensor which performs focusing by driving the focus lens 28 and detectsits stop position. Reference numeral 29 denotes a diopter correctionlens which is retractably placed on the optical axis to focus on thefundus of the eye to be examined which has strong myopia or hyperopiawhich is difficult to focus on with a focus lens. The diopter correctionlens 29 includes a positive diopter correction lens 291 which is aconvex lens and a negative diopter correction lens 292 which is aconcave lens. Reference numeral M4 denotes a diopter correction lensentering/retreating driving motor which causes the negative dioptercorrection lens 292 to enter/retreat (for insertion/removal) withrespect to the imaging optical system 105 if the patient has strongmyopia and causes the positive diopter correction lens 291 toenter/retreat with respect to the imaging optical system 105 if thepatient has strong hyperopia.

Reference numeral 31 denotes an imaging device which photoelectricallyconverts imaging light; 33, an image processing part which outputs thesignal output from the imaging device 31 to a monitor 34 and a systemcontrol part 36. In an internal fixation lamp part 106, a half mirror 30branches an optical path from the imaging optical system 105, and aninternal fixation lamp unit 32 faces the optical path. The internalfixation lamp unit 32 is constituted by a plurality of LEDs and turns onan LED at a position corresponding to the visual fixation part selectedby the examiner. By letting the patient whose eye is being examined fixhis/her vision to the turned-on LED, the examiner can obtain a fundusimage in a desired direction.

A focusing operation member 35 is an operation member used for focusingoperation by the examiner. A focusing operation member position sensorS5 detects the stop position of the focusing operation member 35 andoutputs the detected position to the system control part 36. Note thatin the fundus camera 100, signals from all the sensors described aboveare output to the system control part 36. The system control part 36controls all the motors described above.

FIG. 2 is a schematic view for explaining a focal position detectionmethod using the detection of each focus index shift (to be referred toas a focal position detection method using focus indices hereinafter) asone of focal position detection methods in this embodiment. In otherwords, the shift of a focus index gives rise to information regardingfocal position as will be discussed below. The focal position detectionmethod using focus indices uses two focus indices generated by the splitunit 22. This focal position detection method may be executed by, forexample, the system control part 36. The split unit 22 moves on theoptical axis in synchronism with the focus lens 28 to project twoindices on the imaging device 31. A first focus index image 42 a and asecond focus index image 42 b move in opposite directions with respectto each other as the split unit 22 moves along the optical axis. Whenthe two indices coincide with each other (i.e. when the two focusindices moving toward each other in the vertical direction finally meetin the middle), focusing is understood to have been achieved. Theillumination optical system 103 and in particular the split unit 22 isthus used to enable an examiner to know when focus has been achievedduring the observation phase, but is no longer required once focus hasbeen achieved and the fundus camera enters an imaging phase.

Images 41 a and 41 b in FIG. 2 show the states of the focus indices 42 aand 42 b when the split unit 22 moves in the optical axis. The examinercan observe both the first focus index 42 a and the second focus index42 b in the same image.

Next will be described a method of calculating contrast values describedwith reference to FIG. 2 and a method of detecting a position where afocus index image shift is minimized by using contrast value differencesdepending on the positions of the first and second focus index images 42a and 42 b. The detection of such positions will be described withreference to FIG. 3.

The image 41 a shows the state of scanning for the evaluation of thecontrast of the image. The contrast in this case indicates the luminancedifference between adjacent pixels. A greater contrast value indicates agreater luminance difference. Scan lines are lines indicating aprocedure for obtaining adjacent luminance values and are arranged inparallel and at a constant interval equal to a pixel interval. Acontrast value is the value of the largest luminance difference inluminance data on the scan lines.

Referring to the image 41 a, reference numerals 43 a, 43 b, and 43 cdenote examples of scan lines. In fact, there would be many more scanlines within an image than shown in image 41 a. For example, a focusindex such as 42 a might overlap with 10 scan lines. A method ofdetecting contrast values in the focal position detection method usingfocus indices will be described with reference to these scan lines. Thisfocal position detection method detects contrast values while focusindices are displayed. In this case, a focus index exhibits a higherluminance value than other fundus images such as a blood vessel imageand so the luminance value difference between the focus index and therest of the image can be interpreted as a contrast value. For the sakeof descriptive convenience, we assume that the luminance value of eachfocus index image is constant, and the luminance value of a region otherthan the focus index image is also constant, but with a lower luminancevalue.

On the scan line 43 a, the luminance is constant, because the firstfocus index image 42 a and the second focus index image 42 b are notincluded in the scan line. As a consequence, the contrast value on thescan line 43 a is calculated as 0. On the scan line 43 b, since thesecond focus index image 42 b is included in the scan line, theluminance difference between the portion other than the index image andthe left side surface of the second focus index image 42 b (this “step”from background luminance to focus index luminance being shown ascircled with a dotted line) is calculated as a contrast value on thescan line 43 b. If, for example, the luminance of the portion other thanthe focus index is 0 and the luminance of the second focus index 42 b is100, the contrast value on the scan line 43 b is 100. In addition, onthe scan line 43 c, the luminance difference at the left side surface ofthe first focus index image 42 a is calculated as a contrast value onthe scan line 43 c. Like on the scan line 43 b, the contrast value onthe scan line 43 c is 100.

The contrast value of the entire image 41 a is then calculated by anumber of scanning lines corresponding to the number of pixels in thevertical direction from the upper portion to the lower portion andadding the contrast values obtained on the respective lines. If, forexample, the vertical length of each of the first focus index image 42 aand the second focus index image 42 b corresponds to 10 scan lines, thecontrast value of the entire image 41 a is calculated according to100×10×2=2000. In this manner, the contrast value of the entire image isobtained. That is, the contrast values of the portions in the images 41a to 41 c which are surrounded by the dotted lines are calculated asthose of the respective images.

As described above, the contrast value of the image 41 a is the sum ofthe contrast values of the entire focus index images 42 a and 42 b whichare surrounded by the dotted lines in FIG. 2. Likewise, the contrastvalue of the image 41 b is the sum of the contrast value of the entirefocus index image 42 a and the contrast value of ½ of the focus indeximage 42 b. The contrast value of the image 41 c is equal to that of theentire first focus index image 42 a. Therefore, if, for example, thevertical length of first focus index image 42 a and that of the secondfocus index image 42 b each correspond to the same number of scan lines,i.e., 10 lines, the contrast value of the image 41 a is 100×20=2000.Likewise, the contrast value of the image 41 b is 100×15=1500, and thecontrast value of the image 41 c is 100×10=1000. That is, the image 41 chas the smallest contrast value, the image 41 b has the second largestcontrast value, and the image 41 a has the largest contrast value.

Images 41 d to 41 h in FIG. 3 show the states of the focus index imagesobtained by the imaging device 31, like FIG. 2. The images 41 d to 41 hshow focus index images when the split unit 22 is driven over itsmovable range, and in particular the states of the first and secondfocus index images 42 a and 42 b can be observed. The graph on the lowerpart of FIG. 3 shows the transition of contrast values relative to theposition of the optical-axis direction of the split unit 22 when drivenby the split shift driving motor M1. This graph shows a line connectingpoints corresponding to the contrast values obtained from the respectiveimages 41 d to 41 h.

As described with reference to FIG. 2, the image 41 f in which the shiftbetween the focus index image 42 a and the focus index image 42 b isminimized exhibits the smallest contrast value. That is, the position ofthe split unit 22 at which the image 41 f is obtained coincides with theposition at which the focus index image shift is minimized. It is thuspossible to perform focusing by detecting a position having the smallestof the contrast values obtained from the respective images 41 d to 41 h.

As described above, the focal position detection method using focusindices detects a focal position by using focus indices which areoptically driven in synchronism with the focus lens 28. As describedabove, the focal position detection method using focus indices is aso-called split focusing scheme of calculating a focal position byevaluating the shift between split images (focus index images).

FIG. 4 is a graph for explaining a focal position detection method usingcontrast values as another focal position detection method in thisembodiment. This focal position detection method performs focal positiondetection by evaluating the contrast value of an image of a medium andof a large artery peripheral portion on the retina. Note that the systemcontrol part 36 executes the focal position detection method usingcontrast values. The graph of FIG. 4 shows the position of the focuslens 28 moved in the optical-axis direction by the focus lens drivingmotor M3 and changes in the contrast value of the image signal obtainedfrom the imaging device 31. The method of calculating contrast values isessentially the same as that used in the focal position detection methodusing focus indices described above, but without the focus indices. Inthe focal position detection method using focus indices, the differencesin luminance between the left side surfaces of the focus index images 42a and 42 b and the portion other than the index images are dominant ascontrast components. In contrast, however, the focal position detectionmethod using contrast values displays no focus index images. For thisreason, in the focal position detection method using contrast values,the differences in luminance between a portion other than the medium andlarge artery on the retina and the two end portions of the medium andlarge artery are dominant as contrast components.

As shown in FIG. 4, since an image in an in-focus state becomes sharp,the contrast value is maximized at a focal position F1, whereas thecontrast value is reduced at a position F2 where the amount ofdefocusing is large.

As described above, the focal position detection method using contrastvalues detects a focal position by calculating a position where anactually-captured image exhibits the highest contrast from the imageitself. As described above, the focal position detection method usingcontrast values is a so-called contrast focusing scheme of calculating afocal position by evaluating the contrast of an image. Because contrastdoes not deteriorate with the insertion of a diopter correction lens, afocal position can be detected even if a diopter correction lens isinserted and the optical relationship between the focus lens 28 and thesplit unit 22 deteriorates.

An imaging sequence in the fundus camera 100 will be described belowwith reference to the flowcharts of FIGS. 5A and 5B. When the examinerissues an instruction to start imaging via an operation part (notshown), the system control part 36 executes the processing in step S101and the subsequent steps. First of all, in step S101, the system controlpart 36 turns on the observation light source 16. In step S102, thesystem control part 36 checks whether the diopter correction lens 29 hasentered the imaging optical system 105. If the diopter correction lens29 has not entered the imaging optical system 105, the process advancesto step S103. If the diopter correction lens 29 has entered the imagingoptical system 105, the process advances to step S112.

In step S103, the system control part 36 drives the splitentering/retreating driving motor M2 to cause the split unit 22 to enterthe illumination optical system 103. In step S104, the system controlpart 36 turns on the split LED 221. In step S105, the system controlpart 36 drives the split shift driving motor M1 to move the split unit22 to an initial position. At this time, as described above, the focuslens 28 moves to the initial position in synchronism with the movementof the split unit 22. In step S106, the system control part 36calculates a contrast value by the split focusing scheme described abovewith reference to FIGS. 2 and 3. In step S107, the system control part36 checks whether the split unit 22 is at the end position. If the splitunit 22 is not at the end position, the process advances to step S108.In step S108, the system control part 36 drives the split shift drivingmotor M1 to move the split unit 22 by a predetermined amount. After themovement, the process returns to step S106. At this time, since thesplit unit 22 moves in synchronism with the movement of the focus lens28, the focus lens 28 also moves in accordance with the movement of thepredetermined amount described above.

If the system control part 36 determines in step S107 that the splitunit is at the end position, the process advances to step S109. In stepS109, the system control part 36 drives the split shift driving motor M1to move the split unit 22 to a position where the contrast value isminimized. In accordance with the movement of the split unit 22, thefocus lens 28 also moves to the corresponding position. In step S110,the system control part 36 turns off the split LED 221. In step S111,the system control part 36 drives the split entering/retreating drivingmotor M2 to cause the split unit 22 to retreat from the illuminationoptical system 103.

In step S112, the system control part 36 calculates a contrastevaluation value by the contrast focusing scheme. In step S113, thesystem control part 36 determines whether the contrast evaluation valuecalculated in step S112 is maximized. If the contrast evaluation valueis not maximized, the process advances to step S114. In step S114, thesystem control part 36 moves the focus lens 28 by a predetermined amountby using the focus lens driving motor M3. After the movement, theprocess returns to step S112.

If the system control part 36 determines in step S112 that the contrastevaluation value is at a maximum, the process advances to step S115. Instep S115, the system control part 36 causes the observation lightsource 16 to stop emitting light. The system control part 36 causes theimaging device 31 to start recording in step S116. In step S117, thesystem control part 36 causes the imaging light source 12 to startemitting light. In step S118, the light amount detection part 11 detectsa light amount. In step S119, the system control part 36 checks whetherthe light amount detected by the light amount detection part 11 in stepS118 has reached a predetermined light amount. If the light amount hasnot reached the predetermined light amount, the process returns to stepS118. If the light amount has reached the predetermined light amount,the process advances from step S119 to step S120. In step S120, thesystem control part 36 causes the imaging light source 12 to stopemitting light. In step S121, the system control part 36 stops recordingoperation by using the imaging device 31.

The fundus camera with the above arrangement can perform autofocus evenin a state in which a diopter correction lens is inserted to image thefundus of a patient having strong myopia or hyperopia. That is, thiscamera can perform autofocus regardless of the presence/absence of adiopter correction lens. This facilitates imaging in a suitable in-focusstate.

In the above processing, if the diopter correction lens 29 is notinserted in the optical path of the imaging optical system 105, thecontrast focusing scheme is used after the use of the split focusingscheme. However, the present invention is not limited to this. If, forexample, the diopter correction lens 29 is not inserted in the opticalpath of the imaging optical system 105, the camera might not performfocusing processing based on the contrast focusing scheme.

The above embodiment uses the contrast focusing scheme as the focalposition detection method to be used when the diopter correction lens 29is inserted (the focal position detection method to be executed in stepsS112 to S114). However, the present invention is not limited to this. Itis possible to use any scheme as long as it can evaluate focusingwithout using the split image. That is, when changing the focal positiondetection methods to be used by the system control part 36 in accordancewith whether the diopter correction lens 29 is inserted in the opticalpath of the imaging optical system, this embodiment performs operationas follows:

-   when the diopter correction lens 29 is not inserted in the optical    path, the embodiment uses the split focusing scheme of calculating a    focal position by evaluating the shift between split images; and-   when the diopter correction lens 29 is inserted in the optical path,    the embodiment uses the focusing scheme of detecting a focal    position without using the split image.

As described above, the fundus camera according to the above embodimentcan execute autofocus even in a state in which a diopter correction lensis inserted.

Aspects of the present invention can also be realized by a computer of asystem or apparatus (or devices such as a CPU or MPU) that reads out andexecutes a program recorded on a memory device to perform the functionsof the above-described embodiment(s), and by a method, the steps ofwhich are performed by a computer of a system or apparatus by, forexample, reading out and executing a program recorded on a memory deviceto perform the functions of the above-described embodiment(s). For thispurpose, the program is provided to the computer for example via anetwork or from a recording medium of various types serving as thememory device (for example, computer-readable storage medium).

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2012-237264, filed Oct. 26, 2012, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A fundus imaging apparatus comprising: anillumination optical system configured to project illumination light ona fundus of an eye to be examined; an imaging optical system configuredto guide reflected light from the fundus to an imaging unit; a driveablefocus lens which is provided in an optical path of said imaging opticalsystem and which is configured to focus the reflected light onto theimaging unit; a focusing unit configured to detect a focal position ofthe reflected light based on a signal from said imaging unit and todrive the focus lens according to the detected focal position; and aselection unit configured to select, from a plurality of different focalposition detection methods, a focal position detection method used bysaid focusing unit, wherein a focal position detection method selectedwhen a diopter correction lens is inserted in the optical path isdifferent from a focal position detection method selected when thediopter correction lens is not inserted in the optical path.
 2. Theapparatus according to claim 1, wherein said selection unit isconfigured, when the diopter correction lens is not inserted in theoptical path, to select a split focal position detection method ofcalculating a focal position of the reflected light by evaluating ashift between split images, and wherein said selection unit isconfigured, when the diopter correction lens is inserted in the opticalpath, to use a focal position detection method of detecting a focalposition without using split images.
 3. The apparatus according to claim1, wherein said focusing unit is configured to use at least one of: i) asplit focal position detection method of evaluating a shift betweensplit images; and ii) a contrast focal position detection method ofevaluating a contrast of an image, and wherein said selection unit isconfigured to select between the split focal position detection methodand the contrast focal position detection method in accordance withwhether the diopter correction lens is inserted in the optical path. 4.The apparatus according to claim 3, wherein said selection unit isconfigured to select the focal position detection method to be used bysaid focusing unit so as to use the split focal position detectionmethod and the contrast focal position detection method when the dioptercorrection lens is not inserted in the optical path and to use thecontrast focal position detection method when the diopter correctionlens is inserted in the optical path.
 5. The apparatus according toclaim 3, wherein said selection unit is configured to select the focalposition detection method to be used by said focusing unit so as toselect the split focusing method when the diopter correction lens is notinserted in the optical path and to select the contrast focusing methodwhen the diopter correction lens is inserted in the optical path.
 6. Theapparatus according to claim 5, wherein the contrast focal positiondetection method evaluates a contrast of a fundus image.
 7. Theapparatus according to claim 5, wherein the contrast focal positiondetection method evaluates a contrast in a blood vessel portion.
 8. Amethod of controlling a fundus imaging apparatus, the method comprising:selecting, from a plurality of different focal position detectionmethods, a focal position detection method, wherein a focal positiondetection method selected when a diopter correction lens is inserted inan optical path of an imaging optical system that includes an imagingunit is different from a focal position detection method selected whenthe diopter correction lens is not inserted in the optical path; anddetecting a focal position based on a signal from the imaging unitaccording to the selected focal position detection method.
 9. A methodaccording to claim 8, wherein the selecting step comprises selecting atleast one of a split focal position detection method using split imagesfor determining focal position and a contrast focal position detectionmethod that does not use split images.
 10. The method according to claim8, wherein the selecting step selects a split focal position detectionmethod of calculating a focal position of the reflected light byevaluating a shift between split images when a diopter correction lensis not inserted in the optical path, and wherein the selecting stepselects a focal position detection method of detecting a focal positionwithout using split images when the diopter correction lens is insertedin the optical path.
 11. The method according to claim 8, wherein thedetecting step uses at least one of: i) a split focal position detectionmethod of evaluating a shift between split images; and ii) a contrastfocal position detection method of evaluating a contrast of an image,and wherein the selecting step selects between the split focal positiondetection method and the contrast focal position detection method inaccordance with whether the diopter correction lens is inserted in theoptical path.
 12. The method according to claim 11, wherein theselecting step selects the focal position detection method to be used inthe detecting step so as to use the split focal position detectionmethod and the contrast focal position detection method when the dioptercorrection lens is not inserted in the optical path and to use thecontrast focal position detection method when the diopter correctionlens is inserted in the optical path.
 13. The method according to claim11, wherein the selecting step selects the focal position detectionmethod to be used in the detecting step so as to select the splitfocusing method when the diopter correction lens is not inserted in theoptical path and to select the contrast focusing method when the dioptercorrection lens is inserted in the optical path.
 14. The methodaccording to claim 13, wherein the contrast focal position detectionmethod evaluates a contrast of a fundus image.
 15. The method accordingto claim 13, wherein the contrast focal position detection methodevaluates a contrast in a blood vessel portion.
 16. A non-transitorycomputer-readable medium storing a program for causing a computer toexecute a control method comprising: selecting, from a plurality ofdifferent focal position detection methods, one focal position detectionmethod, wherein a focal position detection method selected when adiopter correction lens is inserted in an optical path of an imagingoptical system that includes an imaging unit is different from a focalposition detection method selected when the diopter correction lens isnot inserted in the optical path; and detecting a focal position basedon a signal from the imaging unit according to the selected focalposition detection method.